This invention relates to cutting webs or strips of an imaging element, and more particularly to improvements in cutting a continuously running web of an imaging element into sections of predetermined length and width without debris generation.
Converting of a web having an image forming layer, typically a silver halide emulsion, into predetermined sizes is a key step in the manufacture of imaging products. Depending on the format of an imaging product, the converting processes generally involve slitting, chopping, and/or perforating. Because of the demands for cleanliness in imaging products, it is critical to minimize dirt generation during the converting processes.
A conventional slitting method employs a plurality of rotating circular blades at predetermined intervals. The rotary blades are arranged side by side in upper and lower pairs so that each pair of upper and lower opposing rotary blades radially overlap each other. The blades rotate in opposite directions but remain engaged with each other, thereby cutting the imaging product into strips. The slitting method is described with reference to FIGS. 1 to 3. FIG. 1 is a front view of a plurality of rotating circular blades mounted on a pair of rollers with a spring load 4 to maintain blade engagement. FIG. 2 is a side view of a pair of rotating blades. FIG. 3 is a sectional view taken along a line Cxe2x80x94C in FIG. 2.
As shown in FIG. 2, upper and lower blades 1 and 2, which are rotating blades of a slitter 3, rotate in the forward direction, as indicated by the arrows, of the running direction of an imaging product web 5. The blades are opposed to each other from the top and bottom surfaces of the imaging product web so as to overlap each other in their radial directions. The upper and lower blades 1 and 2 overlap each other so as to press against each other. Slitting of the web occurs by passing the web between the upper and lower blade 1,2. The pressure between the upper and lower blades is controlled by a predetermined spring load 4.
A guillotine chopper is an apparatus for transversely chopping a continuously moving web of imaging product. The guillotine chopper includes a fixed solid base for supporting the moving web to be cut. A mobile part is mounted in translation with respect to the base. A knife-blade (upper blade) is supported by the mobile part. The mobile part moves in a plane perpendicular to the base and cooperates with a counterblade (lower blade) to cut or slit the imaging product. The knife-blade and counterblade press against each other under a constant pressure controlled by a spring force. The guillotine chopper is with reference to FIGS. 4 to 5. FIG. 4 is a front view of a guillotine chopper. FIG. 5 is the sectional side view taken along a line Cxe2x80x94C in FIG. 4.
As shown in FIG. 4, upper and lower blades 6 and 7 are arranged in the transverse direction of an imaging product web 5. The upper blade 6 moves into the lower blade 7 with a constant shear angle 8 guided and supported by slide 9 on the mobile part 10. A web clamp 11 is positioned prior to the cut point to provide rigid support of the moving web during chopping. The upper and lower blades 6 and 7 are pressed against each other under a constant pressure provided by a spring load 12.
In both rotating blade slitting and guillotine slitting, the upper and lower blades are engaged under a constant force for mechanical stability. Because of this blade contact, zero clearance is achieved for ease of cutting with minimal edge deformation. This blade-blade contact also helps to continuously renew and sharpen the blade tips and surfaces. As shown in FIG. 6, because of the plastic deformation of a ductile imaging element 13, such as a polyester support, the fracture surface protrudes out into the knife path. A piece of support material 14 can then be removed by the upper blade 15 generating skiving debris.
German OLS DE 3829239 published Mar. 9, 1989 suggests modifying the morphology of a polyethylene terephthalate support to achieve clean cutting of a magnetic recording film. U.S. Pat. No. 5,385,704 describes methods to reduce planar orientation of polyethylene terephthalate photographic film base to provide films that are easily cut while generating low quantities of dirt in the process. Although these structural optimizations of a polyethylene terephthalate support for clean cutting are attractive approaches, they do not provide the manufacturing flexibility to cutting systems. It is desirable to provide cutting systems that deliver clean cut edges regardless of the support material employed for an imaging element.
U.S. Pat. No. 5,423,239 discusses slitting a continuous running magnetic tape with a gap between blade edges to prevent burring. With the overall thickness of a magnetic tape ranging from 0.6 to 1.4 mil, this gap was suggested within 0.02 to 0.3 mil. To apply this gap, either the upper and lower blades of a slitter are disengaged and separated with a gap, or maintain engagement but one of the cutting edges is chamfered. For a much thicker imaging film, such as the photographic film, it is mechanically unstable to disengage the upper and lower blades of a slitter due to the higher bending stiffness of the film. While using a chamfered inclined side surface as one of the cutting edges can provide the clearance between blades, this clearance is not a constant but changes with blade penetration into the material. In addition, an inclined surface leads to a point contact between upper and lower blades, thus, accelerating the tip wear. The cutting methods taught by this reference are either impractical for thick imaging elements, deficient in maintaining constant clearance, or prone to higher tip wear. The present invention provides cutting systems that deliver clean cutting without debris generation while avoiding the problems and limitations of the prior art.
It is therefore an object of the present invention to provide a method for slitting and chopping an imaging element whereby it is possible to prevent dirt and skiving generation along the edge of an imaging element while maintaining the engagement between upper and lower blades for mechanical stability but without accelerating the blade wear.
The present invention is a method of cutting an imaging element. An imaging element is moved through a cutting zone formed by a first cutting blade having a first cutting surface and a first engaging surface and a second cutting blade having a second cutting surface and a second engaging surface. In the cutting zone the first engaging surface and the second engaging surface are in contact for a distance greater than or equal to a thickness of the imaging element. The first cutting surface and said second cutting surface are separated by from 1 to 30 percent of the thickness of the imaging element in the cutting zone. The present invention reduces debris and skiving generation.